Fe(III)–humate complexes from Megalopolis peaty lignite: A novel eco-friendly fertilizer

Fe(III)–humate complexes were synthesized from Greek peaty lignite of the Megalopolis Basin. The preparation was carried out under mild and low-energy conditions producing a biodegradable, eco-friendly and effective material to substitute the synthetic chelates Fe–EDDHA, Fe–EDTA and Fe–DTPA. Due to both the existing expanded configuration of the humic substances (that make binding sites accessible to the metal ions) and the ionization of functional groups, alkaline environment facilitates the association between Fe(III) ions and the lignite-derived humic substances. UV–vis and IR spectra revealed coordination of the metal ions with the carboxylic and phenolic groups of the oxygen-rich humic substances. Fe(III)–humate complexes were proved stable in a wide pH range similar to Fe–EDDHA synthetic chelates. Furthermore, the presence of K+ and humic matter increases the agronomic value of this material establishing alternative applications for Megalopolis peaty lignite.